1. Field of the Invention
The present invention relates to an air conditioner for a compartment of vehicles for heating and the like of using a heat pump, and in particular, to an air conditioner mounted on an electric automobile and the like.
2. Description of the Related Art
Because electric automobile and the like which do not include an internal combustion engine, such as a gasoline engine and the like, cannot use the hot water and the like of a radiator as a heat source for heating, the air in a compartment is heated by a heat pump type refrigerant circuit provided with a motor-driven compressor.
Consequently, in such a heat pump type refrigerant circuit, when a heating operation is performed in an environment with a low outside air temperature, the desired amount of heat may not be pumped due to the insufficient heat exchange effected by an external heat exchanger. Further, the desired heating operation may not be carried out because of the forcible stopping of a compressor caused by pressure protection resulting from a drop of pressure on a low pressure side of the circuit.
To solve such problems, an air conditioner has been proposed wherein a circuit is provided for circulating a heat medium, such as water or ethylene glycol water solution heated by a combustion heater, to a heat radiating internal heat exchanger, thereby carrying out a heater-heating operation independent of a heat pump.
In such an air conditioner, however, even if the switching between the heating operation due to the heat pump and the heater-heating operation due to the combustion heater is left to selection of a user, it may be difficult for the user to select one of the operations distinctly from the other. Further, when the operations are simply switched, the temperature of exhaust air is lowered or the distribution of the temperature of the exhaust air is disturbed, and consequently, user comfort may be reduced. Further, there may also be a problem that because the temperature of a heat medium is low at the start of operation and the temperature of the heat medium is more slowly increased as compared with the situation in which air is directly heated, heating may be insufficiently performed immediately after the start of the air conditioner, and cold air is blown into a compartment.
Further, there may also be a problem that because a dehumidification effect may not be obtained in the above-described heater-heating operation, when heating is started in a humid environment, the compartment windows, e.g., the windshield may fog up.